Heat exchanger for gases, especially for engine exhaust gases

ABSTRACT

It comprises a plurality of parallel conduits ( 3 ) provided inside a housing ( 2 ), through which gases to be cooled flow in heat exchange with a cooling fluid, said conduits ( 3 ) being attached between two plates ( 7 ) fixed in both ends of said housing ( 2 ), and the housing ( 2 ), and the housing ( 2 ) and the plates ( 7 ) having an area substantially rectangular.  
     It is characterized in that each plate ( 7 ) comprises dimples ( 9 ) arranged near to its perimeter area, said dimples ( 9 ) including nails ( 10 ) capable of being into contact with a peripherical area ( 11 ) of the housing ( 2 ). It is possible to immobilize the plates during handling and application of brazing paste.

The present invention relates to a heat exchanger for gases, especially engine exhaust gases, of the type comprising a plurality of parallel pipes arranged inside a casing, through which gases flow to be cooled by thermal exchange with a refrigeration fluid, said pipes being connected between two support plates anchored at both ends of said casing, and the casing and the support plates having a substantially rectangular cross-section.

The invention applies particularly to heat exchangers for which the casing, support plates and parallel pipes have a substantially rectangular transverse cross-section. Preferably, it applies to small sized exchangers such as exchangers for the recirculation of engine exhaust gases (EGRC).

PRIOR ART

In some gas cooling heat exchangers, for example those used in systems for the recirculation of exhaust gases to the inlet of an internal combustion engine, the two heat exchanging means are separated by a wall.

More particularly, the gases flow through a series of parallel tubes or pipes arranged inside a casing, and are cooled by thermal exchange with a refrigeration fluid which is made to flow externally to the pipes through which the gases pass.

The tubes are anchored at their ends between two support plates connected at each end of the casing. Both support plates have a plurality of orifices for the placing of the respective tubes.

The gases are fed to the bundle of exchanger tubes from an inlet pipe; given that the diameter of the inlet pipe is smaller than the diameter of the casing and of the bundle of exchanger tubes, between the two there is an inlet tank which gets gradually wider.

Heat exchangers are known for which the casing and support plates have a substantially rectangular cross-section. In this case, assembling the exchanger consists first in pre-assembling the unit formed by the casing, the plurality of tubes and the support plates. Following this, a brazing paste is applied to said unit, the gas tanks are assembled and the complete heat exchanger is furnace welded.

In practice it has been proved that preassembled support plates can be subject to unwanted movements during the assembly of the remainder of the components, given that there is no brazing and no mechanical union between the support plates and the casing prior to the furnace brazing of the whole heat exchanger being completed.

There are some known solutions for immobilizing the support plates during the assembly of the heat exchanger; for example, the support plates may have an edge intended to clamp onto the casing outline, or else, the support plates are clamped by the casing. It is also possible to use furnace brazing or laser brazing to join both components together.

In the case of heat exchangers with a casing and tubes of substantially circular cross-section, a known solution is to make protuberances with a tool like a bradawl on the support plate. On the one hand, the protuberances help the operator to identify quickly the surface which is to be located against the casing, given that said surface is the one which includes the protuberances. On the other hand, said protuberances also have the function of preventing the relative movement of the support plates in respect of the casing during the assembly prior to the furnace brazing. This effect is obtained thanks to the contact by friction of the protuberances with the peripheral zone of the casing, given that the latter have to be made in proximity to the periphery of the support plates.

However, in practice it has proved very difficult to mechanize a casing of absolutely circular cross-section, since there is the risk that some of the protuberances remain outside the peripheral zone of the casing, thereby causing the support plates to move during the assembly prior to the furnace brazing.

DESCRIPTION OF THE INVENTION

The purpose of the present invention is to resolve the above-mentioned drawbacks, developing a heat exchanger that enables the support plates to be immobilized during assembly and brazing of the exchanger.

The heat exchanger for gases, especially engine exhaust gases, which forms the subject matter of the present invention, is of the type that comprises a plurality of parallel tubes arranged inside a casing, through which gases flow to be cooled by thermal exchange with a refrigeration fluid, said pipes being connected between two support plates anchored at both ends of said casing, and the casing and support plates having a substantially rectangular cross-section; and is characterized in that each support plate comprises protuberances arranged in proximity to its peripheral zone, said protuberances including raised portions able to come into contact with a peripheral surface area of the casing.

In this way, thanks to the friction produced between the protuberances and the peripheral surface area of the casing, it is possible to prevent any unwanted movement of support plates during assembly and when applying furnace brazing to the heat exchanger.

To advantage, the protuberances are arranged symmetrically on each support plate. In this way, it is possible to prevent said support plates from rotating.

According to one embodiment of the invention, each support plate comprises at least four protuberances.

Preferably, each support plate comprises six protuberances, four protuberances being arranged at each corner of the support plates, and the two remaining ones arranged in the median area of two opposite laterals.

To advantage, the raised portions of the protuberances are orientated towards the inside of the exchanger in order to assemble the support plates with the casing.

Preferably, the height of the raised portions is 0.5 mm with a tolerance of +0.1/−0.2 mm; the diameter of the protuberances is 2 mm with a tolerance of +0/−0.2 mm; and the distance from the protuberances to the edge of the support plate is approximately 1.05 mm with a tolerance of +0.1/−0 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

To facilitate the description of what has been disclosed above, drawings are appended wherein, diagrammatically and only as a non-restrictive example, a practical embodiment is shown of the heat exchanger for gases, especially engine exhaust gases of the invention, wherein:

FIG. 1 is a diagrammatic longitudinal cross-section of the input zone of a heat exchanger with a conventional tube bundle;

FIG. 2 is a front view of a support plate of rectangular cross-section of the heat exchanger, showing the protuberances which immobilize the support plates relative to the casing of the exchanger;

FIG. 3 is a profile view of the support plate in the figure; and

FIG. 4 is an enlarged view in transverse cross-section of a protuberance.

DESCRIPTION OF A PREFERRED EMBODIMENT

As can be seen in FIG. 1, the heat exchanger 1 is constituted by a casing 2 which contains a bundle of parallel tubes 3, intended for the gases to be cooled to pass through. Inside the casing 2, externally to the tubes 3, flows a cooling fluid, from an inlet 4 to an outlet (not shown).

The gases to be cooled enter the exchanger 1 from a feed pipe 5 and through an input tank 6 which gradually gets wider.

The bundle of tubes 3 is anchored at its ends between two support plates 7 connected at each end of the casing 2, the one located at the inlet being shown in FIG. 1. Each support plate 7 has a plurality of orifices 8 for the placing of the respective tubes 3 (see FIG. 2).

Furthermore, each support plate 7 comprises a group of protuberances 9 arranged in proximity to its peripheral zone. As can be seen in FIGS. 3 and 4, said protuberances 9 include raised portions 10 orientated towards the inside of the casing 2, able to come into contact with a peripheral surface area 11 of the casing 2 (see FIG. 1).

There follows a description of the geometric characteristics of the protuberances 9 according to the present embodiment:

-   -   Six protuberances 9 are made arranged symmetrically, four         protuberances 9 being arranged at each corner of the support         plate 7, and the two remaining ones arranged in the median area         of two opposite laterals.     -   The raised portions 10 of the protuberances 9 are orientated         towards the inside of the exchanger 1 so as to assemble the         support plates 7 with the casing 2.     -   The height of the raised portions 10 is 0.5 mm with a tolerance         of +0.1/−0.2 mm.     -   The diameter of the protuberances 9 is 2 mm with a tolerance of         +0/−0.2 mm.     -   The distance from the protuberances 9 to the edge of the support         plate 7 is approximately 1.05 mm with a tolerance of +0.1/−0 mm.

As for assembling the heat exchanger 1, the first step is to pre-assemble the unit formed by the casing 2, the plurality of tubes 3, and the support plates 7. Following this, a brazing paste is applied to said unit, the gas tanks 6 are assembled, and the complete heat exchanger 1 is furnace brazed.

Through the friction produced between the protuberances 9 and this peripheral surface area 11 of the casing 2, it is possible to immobilize the support plates 7, preventing any unwanted displacement of said plates 7 during the aforementioned pre-assembly, as well as during the assembly of the rest of the components and the final furnace brazing. 

1. Heat exchanger (1) for gases, especially engine exhaust gases, comprising a plurality of parallel pipes (3) arranged inside a casing (2), through which gases flow to be cooled by thermal exchange with a refrigeration fluid, said pipes (3) being connected between two support plates (7) anchored at both ends of said casing (2), and the casing (2) and the support plates (7) having a substantially rectangular cross-section, characterized in that each support plate (7) comprises protuberances (9) arranged in proximity to its peripheral zone, said protuberances (9) including raised portions (10) able to come into contact with a peripheral surface area (11) of the casing (2).
 2. Exchanger (1), according to claim 1, characterized in that the protuberances (9) are arranged symmetrically on each support plate (7).
 3. Exchanger (1), according to claim 1 or 2, characterized in that each support plate (7) comprises at least four protuberances (9).
 4. Exchanger (1), according to claim 3, characterized in that each support plate (7) comprises six protuberances (9), four protuberances (9) being arranged at each corner of the support plate (7), and the two remaining ones arranged in the median zone of two opposite laterals.
 5. Exchanger (1), according to any one of the previous claims, characterized in that the raised portions (10) of the protuberances (9) are orientated towards the inside of the exchanger (1) in order to assemble the support plates (7) with the casing (2).
 6. Exchanger (1), according to any one of the previous claims, characterized in that the height of the raised portions (10) is 0.5 mm with a tolerance of +0.1/−0.2 mm.
 7. Exchanger (1), according to any one of the previous claims, characterized in that the diameter of the protuberances (9) is 2 mm with a tolerance of +0/−0.2 mm.
 8. Exchanger (1), according to any one of the previous claims, characterized in that the distance from the protuberances (9) to the edge of the support plate (7) is approximately 1.05 mm with a tolerance of +0.1/−0 mm. 